International Journal of Aquaculture, 2017, Vol.7, No.16, 106-110
109
Figure 1 Biweekly growth of all male and mixed-sex
Oreochromis niloticus
4 Discussion
The temperature, pH, conductivity and total dissolved solids measured during this study were closely related and
were within recommended range for the culture of tropical fishes as described by APHA (1998). Hence,
application of 17 α-methyltestosterone in the diet
O. niloticus
did not alter the water quality. This study shows that
weight gain for all-male
O. niloticus
were significantly higher than the value recorded for mixed sex tilapia
(P≤0.05). This report is similar to the work of Little et al. (2003), Dan and Little (2000), Mair et al. (1995) and
Abella et al. (1990). Tran-Duy et al. (2008), Dan and Little (2000) had earlier reported that better growth of all
male tilapia is related to the lower energy expenditure on courtship and spawning. However, since no spawning
was observed in the mixed-sex fish during this study (as evident in the number obtained as survival and fairly
uniform size of the experimental fish) other factor may have been responsible for observed performance. It may
be right to infer that the better performance of all male compared to mixed sex tilapia in this study may not be due
to reduced growth as a result of spawning rather its justified by the hypothesis 17 α-methyltestosterone has
growth-promoting actions on tilapia (Shepherd et al., 1997). This was linked to elevations in growth hormone
(GH) metabolism and consequently higher insulin-like growth factors (IGFs). Also, Bhasin et al. (2001) reported
that that testosterone produces muscle hypertrophy by increasing muscle protein synthesis.
The decrease in food conversion ratio (FCR) and an increase in protein efficiency ratio (PER) for all male fish
compared to the mixed-sex fish observed in this study was in accord with the report of Pechsiri and Yakupitiyage
(2005) who reported that FCR decreases while PER increases with increased feeding rate. The underlining
consequence of this is that it would require less feeding to get all male tilapia fish to table size compared to a
mixed sex tilapia. Feed conversion ratio is used to assess feed utilization and absorption. The result of the present
stud shows that all male tilapia had better feed utilization and absorption when compared to mixed sex tilapia and
there was significantly difference (p<0.05) between the treatment. This study negate the report of Sule (2004) and
Guerrero (1985) who reported that there were no significant difference between the food conversion ratio of the
all-male and those of the all-female and the mixed sex population (P≥0.05). The discrepancies in the findings of
these studies may be due to differences in feeding response of the different species, culture system used and feed
type in the experiment. The result of this study shows similar survival rates were observed in both mixed-sex and
all male fish indicating that hormone treatment has no adverse effect on general fish health. This is in agreement
with the report of Cruz and Mair (1994) that 17 α-methyltestosterone treatment have no effect on survival of
tilapia.
5 Conclusion
It may be rightly inferred that 17 α-methyltestosterone treatment of tilapia achieved masculation, higher weight
gain, and it is not toxic to fish at the dosage used in this study. However, the mechanism of better performance as
a result of hormonal administration needs to be clearly understood, hence the need for further research.
